Undeliverable message from former user received when sending Calendar schedule

Hello Experts,

Kind of an odd subject for this Question, but I'll try to explain.
We have a former employee that used to be the administrative assistant to a manager.
This assistant had full control to the managers mailbox, as well as "Send-on-Behalf-Of" permissions.
This user has since left the company, thier user act. and mailbox have been removed.
Whenever someone sends an Outlook Calendar invite to the manager, and even before the manager accepts the schedule entry, an undeliverable message is returned to the invite sending user.
See below example:
Your message did not reach some or all of the intended recipients.
      Subject:      This is a Test Calendar event - so as to post to EE for help in resolving
      Sent:      11/17/2008 10:50 AM
The following recipient(s) could not be reached:
      Manager AssistantUser on 11/17/2008 10:50 AM
            The recipient name is not recognized
            The MTS-ID of the original message is: c=US;a= ;p=MyOrgHere;l=MAIL-081117154937Z-136302

We are getting quite sick of this message, and would like some help to find where it is originating from.
Solutions are welcome.
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Rajith EnchiparambilOffice 365 & Exchange ArchitectCommented:
There is delegation configured in one of the user's Outlook or an Outlook rule. That has to be taken off!

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Rajith EnchiparambilOffice 365 & Exchange ArchitectCommented:
Check Manager's Outlook for any delegation or rules.
I'm guessing that there is either an entry on the users AD properties under "Exchange General" -> "Delivery Options" -> "Forward To"  or there is an inbox rule on the Manager's mailbox that is doign the forwarding.

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Starrett2005Author Commented:
We'll check delegation on the Calendar for the managers Outlook.
Note: This is on an NT4.0 domain

Whoa..  I missed the fact this is a 5.5 server..  Man, I haven't looked at that in SOOOOOOOO long..    There might be something on the 5.5 object that can configure this.  If not, then it's likely something int he Outlook client that is causing this forwarding.
Starrett2005Author Commented:
Thank you
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